The Army is developing propulsion systems to supplement the solid and liquid propulsion systems currently in the field. Airbreathing propulsion has an advantage over solid or bipropellant rockets in that it uses air as the oxidizer and does not have to carry any oxidizer on board; therefore, airbreathing systems offer either longer range or smaller volume. The disadvantage is that the combustion pressures are lower, which prevent airbreathing systems from delivering higher thrust for critical parts of a mission, such as boost and the dash to the target.
Additionally, the Army desires all propulsion systems to have minimum signature exhaust and to meet current Department of Defense (DOD) Insensitive Munitions (IM) Guidelines under Military Standard 2105A.
Conventional ducted rocket solid gas generators containing metal fuels develop high specific impulse when their effluent gases are combusted with air; however, the smoky exhaust gases contain solid particulates that form a smoke trail that does not meet minimum signature properties, which is a requirement for most future Army missile systems. A liquid hydrazine gas generator, which requires a heavy catalyst bed, has lower performance than the smoky solid fuel gas generator. A combination of minimum smoke and high performance is a preferred combination.
An object of this invention is to provide a solid fuel ducted rocket with the capability of increased and variable thrust for the boost and final, or dash, phases of the mission. To accomplish this, this invention contains two key elements:
a) a method to close the air duct and allow higher pressure operation of the combustion chamber that increases net specific impulse; and,
b) The availability of an alternate, high energy gelled oxidizer that combusts with the same fuel gas from the ducted rocket solid fuel gas generator to produce the higher specific impulse (thrust per propellant mass flow rate) required for the boost and dash mission phases.